Problem: $10$ is what percent of $25$ ?
Explanation: Having a percent of something means that you get that percent out of every $100$ We can set up a proportion to find out what percent of $25$ we need to take to get $10$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{\text{part}}}{{\text{whole}}}$ Which things do we know, and what are we trying to find? We are trying to find the ${\text{percent}}$ . Is $25$ the ${\text{part}}$ or the ${\text{whole}}$ The $25$ is the ${\text{whole}}$ . This means the ${\text{part}}$ is $10$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{10}}{{25}}$ If we multiply the denominator of the fraction on the right by $4$ , it will be the same denominator of the fraction on the left. To keep things equal, let's also multiply the numerator on the right by $4$ $ \dfrac{{\text{percent}}}{100 } = \dfrac{{10 \times 4}}{{25 \times 4}}$ $ \dfrac{{\text{percent}}}{100 } = \dfrac{{40}}{{100}}$ $ {\text{percent}} = {40}$ So $10$ is $40\%$ of $25$.